Plugging of copper hollow conductors in water cooled generators is an issue occasionally encountered in large nuclear, fossil and hydro powered power plants, causing load limitations or even unplanned shut-down. A response is the proper choice of stator water chemistry and of the purification systems. The common water chemistry regimes are with low or high oxygen content, and neutral or alkaline pH in the stator water. All these regimes have proven to work in the field, but none is without problems. This can be due to various causes. There is one common trait however: problems arise when the system is being exposed for any length of time to a regime it was not designed for. Stainless steel hollow conductors have only simple requirements on water chemistry. Hollow conductor plugging can lead to overheating and possibly to catastrophic failure, so swift action to remedy the situation is recommended. There are several options. Hot reverse flush can remove debris and temporarily open up the plugs, and mechanical cleaning can open totally blocked hollow conductors. There are several methods for chemical cleaning, the most common being different forms of acid cleaning and EDTA cleaning. The former has the disadvantage of dissolving base metal and brazing as well as the oxides, while the latter method manipulates less aggressive substances that only dissolve the copper oxides in the system.

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